R-1900M (serv.man5). Operation - Sharp Home Appliance Service Manual (repair manual)

r-1900m (serv.man5) service manual
Model
R-1900M (serv.man5)
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3 Few pages! See other manuals at the bottom of the first or last page.
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Service Manual
Brand
Device
Home Appliance / Microwave Oven / Operation
File
r-1900m-sm5.pdf
Date

Read Sharp R-1900M (serv.man5) Service Manual online

R1900M
4 – 1
R1900M
Service Manual
 
CHAPTER 4. 
OPERATION
[1] DESCRIPTION OF OPERATING SEQUENCE 
The following is a description of component functions during oven operation.
1. OFF CONDITION
(For details, refer to Figure O-1)
Closing the door activates the door sensing switch and secondary
interlock switches (1), (2). (In this condition, the monitor switches (1) &
(2) contacts are opened.) When the oven is plugged in, and the rated
voltage is supplied to the switching power supply unit through the
noise filter, (figure O-1). The switching supply unit supplies D.C. volt-
age (approx. 24V) to the relay unit. And the display will show “   .    “.
2. COOKING CONDITION
(For details, refer to Figure O-2)
Press MANUAL/ REPEAT pad. Enter cooking time by pressing the
number pads. Press the POWER LEVEL pad. Enter power level by
pressing the number pad. When the START pad is pressed, the follow-
ing operations occur: 
1. The contacts of relays are closed. And the oven lamp and the
antenna motors connected to the relays are turned on (For details,
refer to Figure O-2).
2. D.C. voltage is supplied to the fan motors, exhaust fan and exhaust
motor from the control unit.
3. Rated voltage is supplied to the primary winding of the power trans-
former and is converted to about 3.00 volts output on the filament
winding, and approximately 2320 volts on the high voltage winding.
4. The filament winding voltage heats the magnetron filament and the
H.V. winding voltage is sent to a voltage doubler circuit.
5. The microwave energy produced by the magnetron is channelled
through the waveguide into the cavity feed-box, and then into the
cavity where the food is placed to be cooked.
6. Upon completion of the cooking time, the oven will revert to the
OFF condition. The fan motors, exhaust fan and the exhaust motor
will operate at least for 1 minute.
7. When the door is opened during a cook cycle, monitor switches (1)
& (2), door sensing switch, secondary interlock switches (1), (2)
and primary interlock relay are activated with the following results.
The circuits to the high voltage components are de-energized. 
8. The monitor switch (1) is electrically monitoring the operation of the
secondary interlock switch (1) and primary interlock relay, and
monitor switch (2) is electrically monitoring the operation of the sec-
ondary interlock switch (2) and primary interlock relay, and monitor
switches (1), (2) are mechanically associated with the door so that
it will function in the following sequence.
1) When the door opens from a closed position, the contacts of the
primary interlock relay and secondary interlock switches (1), (2)
open. Then the monitor switch contacts close.
2) (When the door is closed from the open position, the monitor
switches (1), (2) contacts first open, and then the contacts of the
secondary interlock switches (1), (2) close.
If the secondary interlock switches (1), (2) and primary interlock relay
fail with their contacts closed when the door is opened, the closing of
the monitor switches (1), (2) contacts will form a short circuit through
the monitor fuse, secondary interlock switches (1), (2) and primary
interlock relay, causing the fuse F10 to blow.
3. DOOR OPEN CONDITION
When the door is opened, the contacts of the door sensing switch
open, initiating the following:
1. A signal is input to the control unit energizing the coil of shutoff
relay (RY-4).
2. The shut-off relay (RY-4) contacts close completing circuits to turn
on the oven lamp and antenna motors. 
3. If the door remains open, 60 seconds later the control unit de-ener-
gizes shut-off relay (RY-4) turning off the oven lamp and antenna
motors.
4. VARIABLE POWER COOKING
When Variable Cooking Power is programmed, the rated voltage A.C.
is supplied to the power transformer intermittently through the contacts
of relay (RY-2, RY-3). Relays RY-2 and RY-3 are operated by the con-
trol unit within an interval 54 second time base. Microwave power
operation is as follows:
NOTE: The ON/OFF time ratio does not exactly correspond with
the percentage of microwave power, because approx. 3
seconds are needed for heating of the magnetron fila-
ment.
5. TWO MAGNETRON OPERATION SYSTEM
Two magnetrons (1), (2) are equipped in order to get higher micro-
wave power output. The primary windings of the power transformers
(1), (2) are connected so that each magnetron can be oscillated alter-
natively according to the frequency of the power supply. Refer to the
Figure B-1.
Figure B-1. Operation of Magnetron
VARI-MODE 
ON TIME
OFF TIME
100% 54 
sec.
sec.
90%      
49 sec.
5 sec.
80%      
45 sec.
9 sec.
70%      
40 sec.
14 sec.
60%      
36 sec.
18 sec.
50%      
29 sec.
25 sec.
40%      
24 sec.
30 sec.
30%      
18 sec.
36 sec.
20%      
 13 sec.
41 sec.
10%      
 9 sec.
45 sec.
0%      
 0 sec.
54 sec.
COMMERCIAL
FREQUENCY
(60HZ)
POWER OUTPUT
BY MAGNETRON 1
POWER OUTPUT
BY MAGNETRON 2
OPERATION OF
MAGNETRON
R1900M
4 – 2
[2] DESCRIPTION AND FUNCTION OF COMPONENTS
1. DOOR OPEN MECHANISM
1. The handle lever is pulled.
2. The upper and lower latch heads are lifted up by the linked latch
lever.
3. The latch lever is lifted up by the handle lever.
4. Now both latch heads are lifted up, so they can be released from
the latch hook.
5. Now the door can be opened.
Figure D-1. Door Open Mechanism
2. DOOR SENSING SWITCH
The door sensing switch is activated by the latch head of the door and
switch lever C. When the door is opened, the contacts of the switch
open and interrupt the circuit to the coils of the primary interlock relay.
The contacts of the primary relay then open and interrupt the circuit to
the primary winding of the power transformers.
3. SECONDARY INTERLOCK SWITCHES (1), (2)
The secondary interlock switches (1), (2) are activated by the upper
latch head of the door and switch lever B. When the door is opened,
the contacts of the switch open and interrupt the circuit to the primary
winding of the power transformers (1), (2).
4. MONITOR SWITCHES (1), (2)
The monitor switches (1), (2) are mounted in the upper position of the
latch hook. The monitor switches are activated by the upper latch head
of the door and switch lever A. When the door is opened, the contacts
of the monitor switches close. Monitor switch (1) is intended to render
the oven inoperative by means of blowing the fuse F10, when the con-
tacts of the primary interlock relay and secondary interlock switch (1)
fail to open when the door is opened. Monitor switch (2) is intended to
render the oven inoperative by means of blowing the fuse F10, when
the contacts of the primary interlock relay and secondary interlock
switch (2) fail to open when the door is opened.
Functions:
With the door shut, the contacts of the door sensing switch and the
secondary interlock switches (1), (2) are closed and the contacts of the
monitor switches (1), (2) are open.
1. When the door is opened, the contact of the door sensing switch
and secondary interlock switches (1), (2) are opened first, then the
contact of the monitor switches (1), (2) are closed.
2. As the door goes to a closed position, the contacts of the monitor
switches (1), (2) are opened first, then the contacts of the door
sensing switch and the secondary interlock switches (1), (2) close.
3. If the door is opened, and the contacts of the primary interlock relay
and secondary interlock switch of the same circuit fail to open, the
fuse F10 blows simultaneously with closing of the monitor switch
contacts of that circuit (1 or 2).
CAUTION: BEFORE REPLACING A BLOWN FUSE F10 TEST THE
DOOR SENSING SWITCH, PRIMARY INTERLOCK
RELAY, SECONDARY INTERLOCK SWITCHES (1), (2),
DOOR SENSING SWITCH AND MONITOR SWITCHES
(1), (2) FOR PROPER OPERATION. (REFER TO CHAP-
TER “TEST PROCEDURE”).
5. FUSE F10
1. The fuse F10 blows when the contacts (COM-NO) of the primary
interlock relay (RY1) and secondary interlock switch remain closed
with the oven door open and when the monitor switch closes.
2. If the wire harness or electrical components are short-circuited, this
fuse F10 blows to prevent an electric shock or fire hazard.
3. The fuse also blows when the asymmetric rectifier, H.V. rectifier,
H.V. wire harness, H.V. capacitor, magnetron or secondary winding
of power transformer is shorted.
6. MAGNETRON TEMPERATURE FUSES (1), (2)
The temperature fuses (1), (2) located on the top of the upper and
lower waveguide, are designed to prevent damage to the magnetrons
(1), (2). If an over heated condition develops in the tube due to blower
motor failure, obstructed air ducts, dirty or blocked air intake, etc., the
circuit to the magnetrons are interrupted. Under normal operation, the
temperature fuses remains closed. However, when abnormally high
temperatures are generated within the magnetron, the temperature
fuse will open at 302
°F (150°C) causing the microwave energy to stop.
The defective temperature fuse must be replaced with new rated one.
7. OVEN TEMPERATURE FUSE
The temperature fuse, located on the side of the exhaust duct assem-
bly, is designed to prevent damage to the oven by fire. If the food load
is overcooked, by either error in cook time or defect in the control unit,
the temperature fuse will open. Under normal operation, the oven tem-
perature fuse remains closed. However, when abnormally high tem-
peratures are generated within the oven cavity, the oven temperature
fuse will open at 248
°F (120°C), causing the oven to shut down. The
defective temperature fuse must be replaced with new rated one.
8. EXHAUST THERMISTOR
The exhaust thermistor is located on the side of the exhaust duct
assembly. The temperature in the exhaust duct is detected through the
resistance of the thermistor. If the temperature is high, the control
panel will display”EE7” and the oven will stop to avoid overheating and
catching fire. If the thermistor is open, the control panel will display
“EE8” and the oven will stop.
9. MAGNETRON THERMISTOR
The thermistor is a negative temperature coefficient type. The air tem-
perature around the upper and lower magnetrons is detected through
the resistance of the thermistor. If the temperature is high, the control
panel will display “EE7” and the oven will stop to protect the magne-
trons against overheat. If the magnetron thermistor is open, the control
panel will display “EE8” and the oven will stop.
10. FAN MOTORS
The fan motors drive blades which draw external cool air into the oven.
This cool air is directed through the air vanes surrounding the magne-
trons and cools the magnetrons. This air is channelled through the
oven cavity to remove steam and vapours given off from the heating
foods. It is then exhausted through the exhausting air vents at the
oven cavity. 
Latch hook
Latch
lever
Monitor switch (2)
Secondary
interlock switch (2)
Secondary
interlock switch (1)
Door sensing switch
Monitor switch (1)
Switch lever A
Switch lever B
Switch lever C
Latch
head
Latch
head
Handle
lever
R1900M
4 – 3
During cooking, they operate. After cooking, they will operate at least
for 1 minute and the maximum operating time is 4 minutes. When the
temperature of the magnetron thermistor becomes bellow 110
°C, the
fan motors will stop. These two (2) fan motors are D.C. motors.
11. EXHAUST MOTOR
The exhaust motor is located on the side of the exhaust duct assem-
bly. This motor drives a blade in the exhaust duct assembly. The
driven blade draws the external cool air into the oven from the intake
duct assembly. Then it sends the air out of the oven through the
exhaust duct assembly. During cooking, the exhaust motor operates.
After cooking, it will operate at least for 1 minute and the maximum
operating time is 4 minutes. When the temperature of the exhaust
thermistor becomes bellow 65
°C, the exhaust motor will stop. This
motor is D.C. motor. 
NOTE: Do not disconnect the power supply from the exhaust motor
when it is turned on. Or it may be out of order.
12. ANTENNA MOTORS
The upper and lower antenna motors drive antennas to radiate the
microwave.
13. EXHAUST FAN
The exhaust fan is located to the rear cover. It sends the air (which is
at the top of the oven cavity) out of the oven. This motor is D.C. motor.
14. ANTENNA SENSOR
The antenna sensors are located to the top and bottom of the oven
cavity. And they watch if the antennas are rotating or not.
15. MIROWAVE SENSOR
The microwave sensor is located on the top of the oven cavity. And it
watch if the microwave is radiated into the oven cavity or not.
16. WEAK POINT
If the wire harness or electrical components make a short-circuited,
this weak point blows to prevent an electric shock or fire hazard.
17. H.V. ASYMMETRIC RECTIFIER (1) (2)
The H.V.asymmetric rectifiers (1) (2) are solid state devices that pre-
vent current flow is both directions. And they prevent the temperature
rise of the power transformers (1) (2) by blowing the fuses 12A (1) (2)
when the high voltage rectifiers (1) (2) are shorted. The rated peak
reverse voltage of D1 of the asymmetric rectifier is 6 KV. The rated
peak reverse voltage of D2 of the asymmetric rectifier is 1.7 KV. D1
and D2 of the asymmetric rectifier or high voltage rectifier are shorted
when the each peak reverse voltage goes beyond the each rated peak
reverse voltage. (The process of the blowing the fuse 12A.)
NOTE: The H.V.asymmetric rectifier is assembled with the high volt-
age rectifier actually.
1. The high voltage rectifier is shorted by some fault when microwave
cooking or dual cooking.
2. The peak reverse voltage of D2 of the rectifier goes beyond the
rated peak reverse voltage 1.7 KV in the voltage doubler circuit.
3. D2 of the rectifier is shorted.
4. The large electric currents flow through the high voltage winding of
the power transformer.
5. The large electric currents beyond 12A flow through the primary
winding of the power transformer.
6. The fuse 12A blows by the large electric currents.
7. The power supplying to the power transformer is cut off.
18. OVEN LAMP
The oven cavity light illuminates the interior of the oven so that food
being cooked can be examined visually through the door window with-
out having to open the door. 
19. NOISE FILTER
The noise filter prevents the radio frequency interference that might
flow back in the power circuit.
D2
D1
ASYMMETRIC
RECTIFIER
HIGH VOLTAGE
RECTIFIER
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